How Dortmund bus attacker planned to make millions

The man arrested over an attack on the bus carrying the Borussia Dortmund football team allegedly hoped to make millions off an expected slump in the club's share price by using an obscure financial trade, a "put option".

Such trades are typically used by professional traders at banks or investment firms, suggesting the bomber had some experience with financial markets.

The average person who wants to make money off a dropping share price is likely to take out a bet on one of innumerable gambling websites or use a day-trading website.

"It indicates someone with a bit more financial awareness than your average person," said Chris Beauchamp, senior market analyst at IG Group.

Here are some of the key questions surrounding the suspect's likely plan.

What kind of trade did he use?

Buying "put options" gives the trader the right to buy a stock at a lower price. It is a form of insurance, and is something companies often use to protect themselves against the risk of volatility in financial markets.

Options can be very expensive to buy, although online trading systems now make them accessible to anyone, experts say.

German prosecutors say the 28-year-old suspect took out a five-figure loan to buy thousands of them against Borussia Dortmund's shares on the same day as the April 11 bus attack. The team is the only top-league German club that has shares listed on a stock exchange.

Why such a complicated trade?

Trading experts say it would have been easier to profit from a drop in the share price by simply "shorting" the team's stock through an online trading website. Shorting a stock means selling shares you do not own, with the obligation of buying them back at some point. That can be risky, however, causing big losses if the shares go up instead of down.

While more complicated to trade in, the advantage of a "put option" over "shorting the stock" is that the trader has the right to decide whether - and when - to use it.

If the stock had gone up instead of down, he could simply have cancelled the trade at a relatively low cost.

"He may have wanted to wait and see how the shares reacted and cash in later, for example in case the shares went up in the short-term," said Mr Beauchamp.

Could the suspect have made a lot of money?

In theory, yes, though exactly how much is unclear.

The bombing damage was limited, although one of the team's defenders was injured and had to have surgery. But if the alleged bomber had killed Dortmund team members, that would probably have caused the shares to drop sharply, giving him the opportunity to make a big profit.

The plan, however, was carried out clumsily. The suspect bought the options from a computer at the same hotel where the team was staying. The size and timing of the trade raised the attention of investigators. So even if he had succeeded in causing the shares to drop, he would have been easy to catch.

The plan also seems crude in an age when trading scams tend to rely on more sophisticated - and less deadly - schemes like using insider information or hacking to influence a share price.

Shares in Borussia Dortmund actually rose the day after the bombing attempt and only fell when the team lost its Champions League match later that evening.